NTSB issues 'urgent' recommendations in wake of San Bruno explosion

The September blast in the San Francisco suburb killed eight people and destroyed dozens of homes. The National Transportation Safety Board, which issued the recommendations, has not determined the cause of the blast.

The three key recommendations to local utilities are:

1) Conduct an intensive records search to identify all the gas transmission lines that had not previously undergone a testing regimen designed to validate a safe operating pressure;

2) Determine the maximum operating pressure based on the weakest section of pipeline;

"The NTSB is concerned that the seam-welded sections may not be as strong as the seamless pipe that was indicated in PG&E’s records," officials said in a statement released Monday.

A final report on the causes of the blast is not expected until later this year.

The explosion, one of the deadliest in recent U.S. history, has cost PG&E nearly $250 million in property damage, personal injury compensation, new inspection work and other legal expenses.

The powerful blast occurred after a major transmission line running under a hillside neighborhood began leaking large volumes of gas. When the gas ignited, it blew a 28-foot section of the pipe out of the ground and set fire to more than 50 homes, 37 of which were completely destroyed.

An NTSB report released in December said no evidence of external corrosion, a leading cause of pipeline failures, was found on ruptured sections of the pipe. It does not indicate if internal corrosion was found. But previous reports indicated there did not appear to be significant deterioration of the pipeline wall thickness.